Most HIV vaccine designs are currently based on studies of chronic HIV-1 subtype B infection. However, the prevailing dominance of HIV-1 subtype C (HIV-1 C) in the worldwide AIDS epidemic, and the efficient, albeit temporary, containment of the virus during acute HIV infection necessitates a comprehensive analysis of primary HIV-1 C infection with regard to vaccine design. Assuming that the level of viral set point is dictated by virus-host interactions, we postulated that (i) the kinetics of viral replication, viral diversity, and immune responses vary between primary HIV-1 infections;(ii) virological and immunological determinants in acute HIV-1 infection are related to viral set point, and (iii) virological and immunological parameters in acute HIV-1 infection associated with low viral set point could be identified and targeted for vaccine development. We hypothesize that a combination of functional Gag p24-specific T cell responses and low viral diversity within tat and nef in primary HIV-1 C infection is associated with low viral set point, while lack of functional p24-specific immune response coupled with high tat and nef diversity are markers of high viral set point. To test this hypothesis a prospective study on acute and early HIV-1 infection in Botswana has been designed. There are two Specific Aims in the study: 1. To characterize the magnitude, breadth and kinetics of virological and immunological determinants during primary HIV-1 C infection including transient changes in viral evolution and immune responses. Viral load (RNA and DNA), viral diversity (p24, tat, env, and nef), virus-specific CD4+ and CD8+ T cell immune responses, expression of CCR5 and CXCR4, and levels of beta-chemokine production (MIP-1a, MIP-1B and RANTES) will be analyzed. 2. To assess the association between virological and immunological markers in primary HIV-1 C infection with viral set point. To develop a multivariate model of the inter-relationship of these factors with viral set point.